The present invention relates to unions for tubes of the double wall type i.e. tubes in which the internal duct is surrounded by a chamber or jacket coaxial therewith. The present invention also relates to dies for making said unions.
For example such tubes are used for conveyance of polluting liquids while holding the external jacket under pressure and passing the liquid through the central duct. If the tube is punctured the resulting pressure drop in the external jacket is detected and supply of the conveyed liquid can be promptly stopped.
For such tubes there is the difficulty of providing unions rapidly as it is necessary to ensure continuity both of the duct and the coaxial chamber without leakage between them.
In U.S. Pat. No. 5,398,976 there was proposed a reducer sleeve made of elastomer and having one end with a first diameter suited for receiving a double-wall tube and the other end with a second diameter suited for being traversed only by the internal core of the tube. In a zone intermediate between its ends the sleeve has a connection traversing the sleeve wall and designed for connecting the end of a separate flexible tube with the interior of the sleeve. In use a double-wall tube should be prepared by removing the external wall of the tube from a point onward. The sleeve is fitted on the tube at the terminal end of the external tube wall so that the double-wall tube will enter the sleeve from the end with larger diameter but only the internal core of the tube emerges from the reduced diameter end. The ends of the sleeve are clamped on the tube so that the terminal edge of the tube external wall is sealed inside the sleeve in a zone where the sleeve has the tube connection. In this manner the sleeve seals the air space in the double-wall tube and connects it to the tube grafted to the connection on the outside of the sleeve. According to the contents of U.S. Pat. No. 5,398,976 this sleeve can serve to terminate the external wall of the tube so as to reduce the double-wall tube to a single-wall tube consisting of the internal wall of the double-wall tube. Two double-wall tube sections can be connected by using two sleeves of the above mentioned type to reduce to a single-wall tube the tube ends to be connected and then jointing the single-wall tubes thus obtained with a normal known tube union. The air spaces terminated in the sleeves are connected together by means of a short length of tube with both ends grafted to the sleeve connections.
Such a procedure is clearly laborious and requires rather high manual skill while exposing to risk of leaks due to breakage of the tube core in the uncovered zone between the two sleeves.
The general purpose of the present invention is to overcome the drawbacks of the prior art by supplying unions easy, safe and fast to use for double-wall tubes. Another purpose is to supply dies therefor.
In view of this purpose it is sought to provide in accordance with the present invention a tube union having a first external wall and a second internal wall coaxial with the first to define a chamber around a central duct with the union comprising at least two seats for reception each of one end of a tube to be connected and each seat comprising a first surface designed to adhere to an end segment of the first wall of a tube inserted in the seat and a second surface coaxial with the first and designed to adhere to an end segment of the second wall of said tube with there being between the first and second surfaces of each seat of the union a connection surface with the union comprising at least one first duct leading onto said connection surfaces to provide connection between the chambers of tubes inserted in the seats and at least one second duct leading into spaces circumscribed by the second surfaces to provide connection between the central ducts of said tubes.
Again in accordance with the principles of the present invention it is sought to provide a die for production of unions for double-wall tubes with air space comprising plugs for making seats to receive the ends of the tubes to be jointed and broaches for making ducts for connection of the air space of the tubes when the die is in pressing position with the broaches intersecting the plugs and entering them through the mouthpieces of said seats.